Question

A mutant E. coli strain is found that does not synthesize any enzymes in the presence or absence of lactose (or allolactose). W mutation(s) can lead to this outcome? The lac operon is shown here as a guide. fones where proteins bind DNA genes and regulatory sequences Operator La repressor B-galactosidase B-galactos de transactylase proteins promoter Operator Lacy Lac A laci o Lacz
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Answer 1

The answer should be lac I mutation.

Lac I is responsible for producing the repressor of lac operon. There's a type of mutation in lac I that produces super-repressor of lac operon. This super-repressor can act in cis as well as in trans and has the ability to remain bound to the operator even in presence of an inducer, since, the super-repressor can't be recognized by the inducer. As a result lac operon is switched off even in presence of inducer such as allolactose.